1. Field of the Invention
This invention relates to an aluminum nitride composition which can maintain the electrical insulating properties and high thermal conductivity inherent in aluminum nitride powder even under severe conditions of high temperature and high humidity. More partricularly, it relates to an aluminum nitride composition suited for use in heat dissipation.
2. Description of the Prior Art
In electronic and electric instruments, heat-dissipating greases, heat-dissipating sheets or heat-dissipating coating materials are conventionally used in which a heat-conductive filler having electrical insulating properties have been compounded so that the heat generated in electric parts can immediately be dispersed and transmitted while ensuring electrical insulating properties.
Aluminum nitride powder is characterized by having electrical insulating properties and a high thermal conductivity, and hence widely used as a heat-conductive filler such as heat-dissipating grease.
However, such aluminum nitride powder reacts readily with water, and has a disadvantage that it has moisture resistance so greatly low as to react with atmospheric moisture even in the state it is left in the air, to become decomposed gradually. Thus, there has been a problem that the use of heat-dissipating grease, heat-dissipating sheets or heat-dissipating coating materials compounded with aluminum nitride powder causes a lowering of electrical insulating properties and thermal conductivity because of the decomposition of aluminum nitride.
In order to improve the moisture resistance of this aluminum nitride, methods are proposed in which particle surfaces of aluminum nitride powder are oxidized to provide a protective film of aluminum oxide or particle surfaces of aluminum nitride powder are coated with fused silica. Such methods, however, can not attain any sufficient moisture resistance under severe conditions of high temperature and high humidity.
It is sought to attain a sufficient moisture resistance even under such severe conditions so that the electrical insulating properties and high thermal conductivity inherent in aluminum nitride powder can be well restrained from lowering.